I've seen dozens of these type of cases over the years. Sometimes we can't isolate a cause. It is reasonable to rule out thyroid problems (even in individuals that young)and if everything is OK try dietary supplements and/or diet changes.
Another cause is a chronic yeast infection in the ear and on the skin. Often with these the feet are also affected and there is usually itching, so I'd put that lower on the list of possible causes.
I've found that any oil based salve rubbed on the ear margin helps - it softens the scale and prevents secondary infection. Many use vitamin E ointment.
Doug, DVM